If an air data problem or some other problem results in a reconfiguration to alternate law in an A330, I would think the 'plan' would then be to continue, under control, to point B without stopping off for stall practice. At point B, as the aircraft was slowed and configured, the autotrim would function just as it would in normal law and provide landing configuration trim settings compatible with airspeed. The 330 will fly the approach all the way to 'flare law' in alternate.
As for the 320, I thought someone posted a while back that from alternate law the 320 drops into direct law when the gear is lowered which would require manual trimming on the approach anyway. I may have hallucinated this but I would bet a 320 guy will correct this if I'm wrong (which is a definite possibility) within New York minutes.
Why they're different, I don't have a clue. And preferable, I guess, is in the eye of bestickenholder.
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With respect to absolute separation of LHS & RHS control input devices:
In the case of a column/wheel 'jam' (possible cable/control surface jam) in a follow-up 'connected' yoke system, the older non-FBW Boeings had both fast and slow speed electrical trim switches for pitch control thru the stab with a jammed elevator or hand flown elevator control with a jammed stab. As far as roll, they had a force breakout shear system for the right side control wheel which allowed direct control of the spoiler mixer by the right-seater for roll.
The pilot actuated electric trim (no pilot actuated electric slow speed trim in the 73) is obviously carried on in later Boeings but I don't know about the shear-out capability for the control wheel, but I would suspect there is a provision for independent roll control of some sort. Could be wrong of course.
